<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>

  <!-- h1/p/div -->
  <!-- span/a/img/strong -->

  <div>
    <h1></h1>
    <p></p>
    <a href=""></a>
    <img src="" alt="">
  </div>

  <!-- 不要在p元素中放div元素 -->
  <p>
    123
  <div>我是div</div>
  abc
  </p>

  <!-- 行内级元素不要放块级元素 -->
  <span>
    321
    <div></div>
    <p></p>
    cba
  </span>

</body>

</html>